Reconstruction of diseased segments of the vascular system comprises a major area of cardiovascular research. Technical difficulties increase as one attempts to bypass lesions in small internal diameter vessels. The lack of compliance, i.e., lack of expansile characteristics of vascular substitutes, has recently been cited as a major defect in current prosthetic materials. The purpose of the proposed research is to systematically study the effect of compliance on vascular prosthetic function in an in vivo model in the mongrel dog. In vivo compliance of vascular segments will be determined using electromagnetic rheoangiometry. This equipment allows continuous intraluminal measurement of change in diameter, flow rate, and blood pressure without requiring exposure of the segment to be studied. Microporous polymeric vascular prosthetics will be fabricated to approximate, over and under approximate the compliance of autogenous arterial segments. Short-term implant studies will be conducted initially to evaluate effects at the vascular interface and anastomotic sites. The second phase of the study will be to evaluate long term effects of mismatch in compliance and its relationship to common complications of vascular prothetic materials. Autogenous vein remains the preferred substitute for replacement of vascular lesions in small caliber vessels, although with long-term implantation they undergo degenerative changes of myointimal hyperplasia and luminal narrowing. An additional objective of the proposed research is to study the progression of these degenerative events as they relate to mismatches in dynamic compliance of artery to vein anastomoses, and to the effect of devascularization of vein segments at the time of harvest.